Control indicates 'Low Water' or 'LWCO'; burner is disabled and may show a lockout or alarm condition.

Safety first: Turn off power. Hot water and steam can cause severe burns. Do not open any relief valves while the system is hot or under pressure.

• Check system pressure: Read the pressure gauge on the water heater or associated boiler. For most hydronic systems, cold pressure should be around 12–15 psi (check your manual). If pressure is low, the system may need to be refilled and purged.
• Inspect for leaks: Look for visible leaks at piping, valves, and around the water heater. Repair leaks before refilling.
• Verify automatic fill valve operation: If your system has a pressure-reducing fill valve, ensure the manual shutoff to it is open and that the valve is not clogged. Manually operate the fast-fill lever if present to restore pressure.
• Clean LWCO probe (if accessible): On probe-type low water cutoffs, mineral buildup can insulate the probe. With power off and system drained or isolated as required, remove the probe and clean it with a non-abrasive pad. Reinstall with new gasket if needed.
• Reset and test: After restoring proper water level and pressure, reset the LWCO or control. If the low water indication persists, the LWCO device may need replacement.